Correcting for ascertainment bias in the COGA data set

The effects of several corrections for ascertainment bias on a linkage resu lt in the COGA data are examined. A correction that models the complete asc ertainment protocol markedly reduces the evidence for linkage. Different pa rtial corrections increase the linkage signal and recover good estimates of the population trait prevalence, but do not represent adequately the compl exity of the COGA ascertainment scheme. Evidently the present size of the C OGA data set cannot support a complete correction for ascertainment bias, b ut an effective partial correction can and should be implemented. (C) 1999 Wiley-Liss, Inc.